The present invention relates generally to communications systems, and more specifically, to systems and techniques for acquisition of a gated pilot signal.
Modern communications systems are designed to allow multiple users to share a common communications medium. One such communications system is a code division multiple access (CDMA) system. The CDMA communications system is a modulation and multiple access scheme based on spread-spectrum communications. In a CDMA communications system, a large number of signals share the same frequency spectrum and, as a result, provide an increase in user capacity. This is achieved by transmitting each signal with a different pseudo-noise (PN) code that modulates a carrier, and thereby, spreads the spectrum of the signal waveform. The transmitted signals are separated in the receiver by a correlator that uses a corresponding PN code to despread the desired signal""s spectrum. The undesired signals, whose PN codes do not match, are not despread in bandwidth and contribute only to noise.
In a CDMA communications system, a subscriber station may access a network, or communicate with other subscriber stations, through one or more base stations. Each base station is configured to serve all subscriber stations in a specific geographic region generally referred to as a cell. In some high traffic applications, the cell may be divided into sectors with a base station serving each sector. Each base station transmits a continuous pilot signal which is used by the subscriber stations for synchronizing with a base station and to provide coherent demodulation of the transmitted signal once the subscriber station is synchronized to the base station. The subscriber station generally establishes a communications channel with the base station having the strongest pilot signal.
Since a continuous pilot signal requires bandwidth that could otherwise be used to transmit information, some recently developed CDMA communications systems have employed gated pilot signals. By gating the pilot signal, additional bandwidth can be realized which increases the capacity of the base station. However, synchronizing the subscriber station to the gated pilot signal can be highly inefficient because the subscriber station may spend considerable resources searching for the pilot signal during periods where none is present.
In one aspect of the present invention, a method of acquiring a gated pilot signal includes searching for a first gated pilot signal, deriving timing information from the search for the first gated pilot signal, and searching for a second gated pilot signal using the timing information.
In another aspect of the present invention, a receiver includes a searcher configured to generate a bit sequence, a correlator configured to correlate a received signal with the bit sequence, and a processor configured to detect a first gated pilot signal as a function of the correlation, derive timing information from the first gated pilot signal, and detect a second gated pilot signal by using the timing information to control the bit sequence generated by the searcher.
In yet another aspect of the present invention, computer-readable media embodying a program of instructions executable by a computer performs a method of acquiring a gated pilot signal, the method including searching for a first gated pilot signal, deriving timing information from the search for the first gated pilot signals, and searching for a second gated pilot signal using the timing information.
In a further aspect of the present invention, a receiver includes first detection means for detecting a first gated pilot signal, timing means for deriving timing information from the first gated pilot signal, and second detection means for detecting a second gated pilot signal by using the timing information.
In yet a further aspect of the present invention, a method of acquiring a gated pilot signal includes searching for a plurality of first gated pilot signals each comprising a bit sequence from a first coset, deriving timing information from the search for the first gated pilot signals, and searching for a plurality of second gated pilot signal using the timing information, each of the second gated pilot signals comprising a bit sequence from one of a plurality of cosets other than the first coset.
In another aspect of the present invention, a receiver includes a searcher configured to generate a bit sequence, a correlator configured to correlate a received signal with the bit sequence, and a processor configured to search for a plurality of first gated pilot signals by sequencing the searcher through a plurality of first bit sequences from a first coset, derive timing information as a function of the correlation of the received signal with each of the bit sequences from the first coset, and searching for a plurality of second gated pilot signals by sequencing the searcher through a plurality of bit sequences from each of a plurality of cosets other than the first coset and controlling the correlation thereof with the received signal as a function of the timing information.
In yet another aspect of the present invention, a method of establishing a communications channel includes transmitting from each of a plurality of first base stations a first gated pilot signal each comprising a bit sequence from a first coset, transmitting from each of a plurality of second base stations a second gated pilot signal each comprising a bit sequence from one of a plurality of cosets other than the first coset, searching from a subscriber station for the first gated pilot signals, and deriving timing information from the search for the first gated pilot signals, searching from the subscriber station for the second gated pilot signals using the timing information, and establishing a communications channel between the subscriber station and one of the first and second base stations based on the search for the first and second gated pilot signals.
It is understood that other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein it is shown and described only exemplary embodiments of the invention by way of illustration. As will be realized, the invention is capable of other and different embodiments and its several details are capable of modification in various other respects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive.